Defect inspection system

ABSTRACT

A defect inspection system can suppress an effect of light from a sample rough surface or a regular circuit pattern and increasing a gain of light from a defect such as a foreign material to detect the defect on the sample surface with high sensitivity. When a lens with a large NA value is used, the outer diameter of the lens is  10   a , and an angle between the sample surface and a traveling direction of the light from a defect is α 1 . An oblique detection optics system receives the light from the defect at a reduced elevation angle α 2  with respect to the sample surface to reduce light from the sample rough surface, an oxide film rough bottom surface, and a circuit pattern, and to increase the amount of the light from the defect and detected. The diameter  10   a  of a lens is smaller than the diameter  10   b , resulting in a reduction in the ability to focus the scattered light. When a lens with an outer diameter  10   c  is used to improve the focus ability, the lens interferes with the sample. To avoid the interference, a portion of the lens interfering with the sample is removed. The lens has an aperture larger than the diameter  10   b  while the lens receives the light scattered at the elevation angle α 2 , making it possible to improve the ability to detect defects and lens performance simultaneously.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a defect inspection system fordetecting a foreign material and a defect produced in a process formanufacturing a large scale integration (LSI) semiconductor device or aflat display substrate.

2. Description of the Related Art

In the process for manufacturing a semiconductor LSI, for example, aforeign material or a defect pattern present on a substrate (wafer) maycause a malfunction such as a short circuit and insulation. With thetendency of reducing the size of a semiconductor element, a microforeign material and a defect pattern cannot be ignored as the cause ofthe malfunction. Therefore, the importance of the following technique isincreased: a technique for inspecting a foreign material and a defectduring the process for manufacturing a semiconductor wafer and formanaging the yield in order to take measures for reducing defects.

Defect inspection techniques are mainly divided into two methods, abright field imaging method and a dark field imaging method. The brightfield imaging method is to illuminate a sample and detect light(zero-order diffracted light) specularly reflected from the sample,while the dark field imaging method is to detect scattered light,without detecting the light (zero-order diffracted light) specularlyreflected from the sample.

Each of JP-A-2005-283190 and Japanese Patent No. 3566589 discloses atechnique using the dark field imaging method. JP-A-2005-283190describes a technique for using a plurality of illumination sections andswitching between light paths of the illumination sections based on thetype of a foreign material or a defect. Japanese Patent No. 3566589describes a technique for illuminating a sample substrate having acircuit pattern formed thereon with beams substantially parallel to eachother in a longitudinal direction of an elongated beam spot formed bythe beams, the beams propagating in a direction corresponding to apredetermined angle with respect to a normal to the substrate, apredetermined angle with respect to main straight lines of the circuitpattern and a substantial right angle with respect to the direction ofscanning the sample substrate mounted on a stage.

SUMMARY OF THE INVENTION

The defect inspection technique using the dark field imaging method isto improve inspection sensitivity by receiving a large amount of signalsoutput from a defect to be scanned and to suppress signals output fromother parts such as a regular circuit pattern on the surface of asubstrate.

The principle of a dark field imaging method related to the presentinvention will be clarified. First, a sample is opaque to anillumination light beam. The illumination light beam incident on thesample is specularly reflected, diffracted, or scattered (above thesample (in an upper hemisphere)) on the surface of the sample, or aforeign material or a defect. It is preferable that light derived fromthe foreign material or the defect be detected and that light derivedfrom other parts such as a regular circuit pattern on the surface of thesubstrate be not detected. To achieve this preferable configuration, theincident direction (defined by an elevation angle formed between thedirection of traveling of the illumination light beam and the surface ofa sample and an azimuth angle formed between the direction of travelingof the illumination light beam and a specified direction) of theillumination light beam is specified, and the receiving direction(defined by an elevation angle formed between the direction of travelingof light scattered from the sample and the surface of sample and anazimuth angle formed between the direction of traveling of the lightscattered from the sample and the specified direction) of light to bereceived by a detection system is determined. The incident direction ofthe illumination light beam and the receiving direction of light to bereceived by the detection system in the upper hemisphere characterizedefect inspection techniques provided in respective optics systems.

An actual defect inspection system encounters problems in theabovementioned principle and in the mechanical configuration of anoptics system. In other words, it is necessary that a limitation of aninstallation space be considered.

Regarding conventional techniques, an optical lens (objective lens) forreceiving light, which is shown in FIGS. 12 and 13 of Japanese PatentNo. 3566589, has a circular shape. The circular lens is provided in acasing (refer to FIG. 1 of JP-A-2005-283190). This causes a limitationof an installation space, causing difficulty in improvement ofinspection sensitivity.

To avoid the above problem, a technique for covering the entire surfaceof the upper hemisphere with a small-diameter fiber can be considered.This technique, however, causes the configuration of the system to becomplicated, and has not been put into practical use yet.

It is, therefore an object of the present invention to provide a defectinspection system capable of detecting a defect and the like present onthe surface of a sample with high sensitivity by suppressing an effectof light scattered from a rough surface of the sample and a regularcircuit pattern and increasing a gain of the light scattered from adefect or a foreign material.

According to the present invention, an optical lens is arranged betweena sample to be inspected and detection unit for detecting lightscattered from the surface of a sample which is irradiated with anillumination light beam. The optical lens focuses the scattered light onthe detection unit. The length in the azimuth direction is made largerthan the length in the elevation direction with respect to the surfaceof the sample to be inspected

The defect inspection system according to the present invention iscapable of suppressing an effect of light scattered from a rough surfaceof the sample to be inspected and a regular circuit pattern andincreasing a gain of the light scattered from a defect and a foreignmaterial to detect a defect and the like present on the surface of asample with high sensitivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top view of an optics system for detection, explaining theprinciple of the present invention.

FIG. 1B is a diagram showing the configuration of the optics system fordetection, explaining the principle of the present invention.

FIGS. 2A and 2B are each a diagram showing the positional relationshipbetween the optics system for detection and an optics system forillumination, explaining the principle of the present invention.

FIGS. 3A to 3C are each a diagram showing characteristics ofdistribution of light reflected on and scattered from a defect and aback surface of a thin film, explaining the principle of the presentinvention.

FIGS. 4A to 4E are each a diagram showing the relationship between anaperture of the lens for detection and an elevation angle of an opticallens for detecting in oblique direction.

FIGS. 5A and 5B are each a diagram showing a semiconductor wafer withLSI arranged thereon, which is an inspection sample of the presentinvention.

FIG. 6 is a diagram explaining an effect of the present invention.

FIGS. 7A and 7B are each a diagram explaining a difference in effectbetween an adjusted elliptical lens according to the present inventionand a circular lens.

FIG. 8 is a diagram showing an example of an arrangement in which aplurality of the adjusted elliptical lenses are provided at positionscorresponding to elevation angles different from each other, explainingthe effect of present invention.

FIG. 9 is a diagram explaining the effect of the present invention.

FIGS. 10A to 10C are each a diagram showing a modification of anembodiment of the present invention.

FIGS. 11A to 11C are each a diagram explaining a difference in defectaccumulation between illumination at a low elevation angle with respectto the surface of the sample and illumination at a high elevation anglewith respect to the surface of the sample.

FIG. 12 is a diagram showing an example of a modification of the presentinvention.

FIG. 13 is a diagram showing another example of the modification of thepresent invention.

FIG. 14 is a diagram showing the configuration of a defect inspectionsystem applied to the present invention.

FIG. 15 is a diagram showing three beam spot imaging sections of theoptics system for illumination.

FIGS. 16A and 16B are each a diagram explaining a method for forming anelongated beam spot.

FIG. 17 is a diagram explaining the method for forming the elongatedbeam spot.

FIG. 18 is a diagram showing an example of the arrangement of three beamspot imaging sections provided in the optics system for illumination.

FIG. 19 is a diagram showing an optics system for detection of lightscattered upwardly with respect to the surface of the sample.

FIG. 20 is a diagram showing an example of a modification of the opticssystem for detection of light scattered at a right angle and almostright angle, as shown in FIG. 19.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described with referenceto the accompanying drawings.

First, the principle of the present invention will be described. FIG. 1Ais a top view of an optics system (hereinafter referred to as a“detection optics system”) for detection of light. FIG. 1B is a diagramshowing the configuration of a system for efficiently detecting adistribution of light scattered from a defect present on a siliconwafer. In FIGS. 1A and 1B, a wafer to be inspected is placed on a samplescanning mechanism 600, and is illuminated by an optics system forillumination with an illumination beam 2 from an oblique direction withrespect to the surface of the silicon-wafer. The optics system has anoptical source 1. The illumination beam 2 is distributed on the siliconwafer to form, on the silicon wafer, a beam spot having an elongatedshape with a longer axis perpendicular to a direction of scanning of astage. If a defect is present on the silicon wafer, the light 4scattered from the defect is received by an optics system (a lens 10)for detection. The detection optics system is arranged at a position toensure that an imaginary line extending between the center of the lens10 and the center of a beam spot is inclined with respect to the surfaceof the silicon wafer. An optical image obtained by the detection opticssystem is converted into an electrical signal by a photoelectricconverter 5. A part of the electrical signal is transmitted through asignal receiver 604 directly to a signal processor 606, and processed bythe signal processor 606. The remaining part of the electrical signal istransmitted through a reference signal memory 605 to the signalprocessor 606. The signal processor 606 is designed to detect a defect,determine whether the defect is true or false, classify the type of thedefect, and determine the shape of the defect.

A system controller 602 controls a series of the signal processing,operations for the above-mentioned determinations, a command to amechanism controller 601, and transmission and reception of a signalfrom and to a user interface 603.

Next, FIGS. 2A and 2B are each a diagram explaining the positionalrelationship between an optics system for illumination and the detectionoptics system. In FIG. 2A, an optical source 1 drawn on the left bottomside of FIG. 2A emits an illumination light beam 2. In this case, theillumination light beam is specularly reflected on the wafer to formlight 3, which travels in a direction on the right top side of FIG. 2A.The optics system (hereinafter referred to as the “oblique detectionoptics system”) for detection of light scattered at an acute angle withrespect to the surface of the sample can be installed in any azimuthdirection with respect to the center of the beam spot formed on thewafer (in a horizontal direction with respect to the surface of thewafer) to ensure that the specularly reflected light 3 is not receivedby the oblique detection optics system. FIG. 2B is a side view of thearrangement with the optics system for illumination and the detectionoptics system. The following two angles can be adjusted: the incidentangle (elevation angle) of scattered light 4 emitted by the opticssystem for illumination with respect to the surface of the wafer; andthe output angle (elevation angle) of the scattered light 4 with respectto the surface of the wafer. To detect a defect with high sensitivity,the value of the elevation angle is set to be low since a signal with ahigh signal-to-noise ratio is detected from the defect.

FIGS. 3A to 3C are diagrams each showing a distribution of lightscattered from a rough surface of a wafer. In FIG. 3A, the surface of awafer 7 is illuminated with the illumination light beam 2 from anoblique direction, and light 20 a scattered from a defect 20 isintensively distributed into a space, which is similar to a space of thedistribution of the illumination light beam 2 specularly reflected. Asshown in FIG. 3B, light 21 a is scattered from a rough surface 21(regular portion) of the wafer 7, such as grains, and is relativelywidely distributed. The amount of components of the light 21 a directingto a detector 5 is small.

Thus, the detector 5 is installed to ensure that the optics systemdetects the light scattered at a low elevation angle with respect to thesurface of the wafer 7, resulting in the fact that the amount of thelight scattered from the rough surface of the wafer 7 is small and theoblique detection optics system effectively receives a signal from thedefect. As shown in FIG. 3C, if the surface of the wafer 7 is coveredwith a transparent oxide film, the amount of light 22 c reflected fromthe defect 22 at a low elevation angle with respect to the surface ofthe wafer 7 is smaller than that of light 22 a reflected from the defect22 at a high elevation angle with respect to the surface of the wafer 7at an interface 7 a of the oxide film due to reflectivity of the surfaceof the oxide film and distribution of transmissivity (since light 22 breflected from the defect 22 is separated from the light 22 c). In thiscase, it is necessary that the detector 5 be installed in the vicinityof the wafer 7 to receive light reflected from the defect 22 at a lowelevation angle with respect to the surface of the wafer 7 since thedetector 5 detects a signal coming from the defect 22 on a bottomsurface of the oxide film with high sensitivity and with lowsusceptibility to light scattered from the rough bottom surface of thetransparent oxide film 7 a or a circuit pattern.

FIGS. 4A to 4 e each show the configuration of the detection opticssystem in the case of detection of light scattered at an acute anglewith respect to the surface of the wafer 7. If the detection opticssystem detects light with high sensitivity, an angle of an aperture forreceiving light from a lens needs to be large. FIG. 4A shows an opticssystem with a lens having a large numerical aperture (NA). In FIG. 4,the outer diameter of the lens is a value of 10 a, and an angle formedbetween the surface of the wafer 7 and a direction of traveling of thelight 4 is a value of α1. FIG. 4B shows the case where the obliquedetection optics system receives the light 4 reflected from the defectat a reduced elevation angle α2 with respect to the surface of the wafer7 to reduce light scattered from a rough surface of the wafer 7, a roughbottom surface of the oxide film, and a circuit pattern, and to increasethe amount of the light, which is scattered from the defect and is to bedetected. In this case, the elevation angle α2 can be set to be smallerthan the elevation angle α1. The outer diameter 10 b of the lens,however, is smaller than the outer diameter 10 a of the lens. As aresult, the lens having the outer diameter 10 b has a lower ability tofocus the scattered light than that of the lens having the outerdiameter 10 a.

If the lens shown in FIG. 4C has an outer diameter 10 c similar to theouter diameter 10 a shown in FIG. 4A to increase the ability to focusthe scattered light, the lens interferes with the wafer 7.

To avoid the interference, a portion of the lens, which interferenceswith the wafer 7, is removed. The lens with the portion removed is shownin FIGS. 4D and 4E. The removal of the portion which interferences withthe wafer 7 allows the lens to have an aperture larger than that of thelens having the outer diameter 10 b while the elevation angle α2 ismaintained. This makes it possible to improve the ability to detect thescattered light and performance of the lens simultaneously. In FIG. 4E,a portion of the lens shown in FIG. 4D, which is located on the oppositeside of the removed portion, is removed to form an adjusted ellipticallens. The adjusted elliptical lens shown in FIG. 4E can reduce itsvolume in an elevation direction parallel to a normal to the directionof traveling of the light 4 reflected from the sample at the elevationangle α2. The adjusted elliptical lens allows the oblique detectionoptics system with high lens performance to be installed. The opticssystem is also assembled with high density implementation in anelevation direction. A plurality of the oblique detection optics systemsmakes it possible to increase information to be detected from a defect,resulting in the fact that the ability to detect the defect and theability to classify the type of the defect can be improved.

Next, a description will be made of the definition of the shape of theadjusted elliptical lens. The adjusted elliptical lens has a shapeobtained by cutting a circular lens by use of two cutting lines parallelto each other. The adjusted elliptical lens has two straight sidesparallel to each other and two elliptical arcs located symmetrically toa central axis thereof, which is perpendicular to the two straightsides. The distance between the two straight sides is smaller than themaximum length of an imaginary line extending between the two ellipticalarcs, the imaginary line being parallel to the two straight sides.

As examples of values of the optics system, the NA in an elevationdirection (parallel to a normal to the direction of traveling of thelight, which is scattered from the sample and is to be detected by theoptics system) can be 0.12, the NA in an azimuth direction (parallel tothe surface of the sample) can be 0.45, and the elevation angle can be12 degrees.

Next, with reference to FIGS. 5A and 5B, a description will be made of asample to be inspected by a defect inspection system according to thepresent invention.

A semiconductor wafer 1 a shown in FIG. 5A has chips 1 aatwo-dimensionally arranged at a predetermined interval. Each of thechips 1 aa is composed of a memory LSI. Each of the chips 1 aa mainlyincludes: a memory cell area lab; a peripheral circuit area 1 accomposed of a decoder, a control circuit and the like; and another arealad. The memory cell area lab has a repetitive memory cell pattern withmemory cells regularly arranged in a two-dimensional manner. Theperipheral circuit area 1 ac has a non-repetitive pattern with circuitsirregularly arranged in a two-dimensional manner.

A semiconductor wafer 1 b shown in FIG. 5B has chips 1 ba, each of whichis composed of LSIs such as microcomputers two-dimensionally arranged ata predetermined interval. Each of the chips 1 ba mainly includes: aregister area 1 bb, a memory area 1 bc, a central processing unit (CPU)core area 1 bd, and an input/output area 1 be. FIG. 5B is a conceptualdiagram showing the arrangement including the memory area 1 bc, the CPUcore area 1 bd and the input/output area 1 be. The register area 1 bbhas a repetitive pattern with registers regularly arranged in atwo-dimensional manner, and the memory area 1 bc has a repetitivepattern with memories regularly arranged in a two-dimensional manner.The CPU core area 1 bd has a non-repetitive pattern with CPU coresirregularly arranged, and the input/output area 1 be has anon-repetitive pattern with input/output sections irregularly arranged.As described above, the samples 1 to be inspected by the defectinspection system according to the present invention, which are thesemiconductor wafers 1 a and 1 b shown in FIGS. 5A and 5B respectively,have chips regularly arranged. In each of the chips, the minimum linewidth varies depending on the area. Also, some of the areas each have arepetitive pattern and the remaining areas each have a non-repetitivepattern. Various configurations can be considered depending on theareas.

Next, a description will be made of effects of the oblique detectionoptics system using the adjusted elliptical lens shown in FIG. 4D andthe oblique detection optics system using the adjusted elliptical lensshown in FIG. 4E when the sample shown in FIG. 5A or the sample shown inFIG. 5B is used.

Effect 1

It is possible to install the oblique detection optics system with ahigh numerical aperture (aperture ratio) at a position corresponding toa low elevation angle formed between the direction of traveling of lightscattered from the sample and the surface of the sample. As shown inFIG. 6, the oblique detection optics system is configured to ensure thatthe sample is illuminated with light through illumination lenses 110,120 and 130 and that a detector 501 detects light scattered from thesample through an adjusted elliptical lens 502. In the oblique detectionoptics system, an aperture angle of the adjusted elliptical lens can belarge in the horizontal direction (parallel to the surface of thesample) to improve the optical performance.

With reference to FIGS. 7A and 7B, a circular lens 10A mounted in acasing 30 and an elliptical lens 10B mounted in a casing 31 are comparedwith each other. If an elevation angle is α2 in FIGS. 7A and 7B, theaperture angle of the elliptical lens 10B can be larger than that of thecircular lens 10A in the horizontal direction.

Effect 2

It is possible to detect a high signal-to-noise ratio since thenumerical aperture is determined based on the difference betweencharacteristics of the scattered light.

Returning back to FIGS. 3A to 3C, it is understood that, in the casewhere the sample is illuminated with the light beam from the obliquedirection, and light scattered from the sample is detected in adirection other than the direction of traveling of the specularlyreflected light, the ability to detect the light can be improved byreducing the aperture angle in the elevation direction to reducebackground noise caused by irregular grains and increasing the apertureangle in the azimuth direction to increase the amount of the lightscattered from the defect. It is, therefore, understood that theadjusted elliptical lens is optimal to detect the scattered light withhigh sensitivity.

The above description was made of the oblique detection optics system inwhich the light reflected at a low elevation angle with respect to thesurface of the sample is detected. However, it has been reported that itis effective to detect a defect present on a part of a pattern by usingthe optics system for irradiating the illumination light beam at a highelevation angle with respect to the surface of the sample, and theoptics system (hereinafter referred to as the “upward detection opticssystem) for detection of light scattered upwardly with respect to thesurface of the sample. In this case, it is possible to improve theability to detect the scattered light by using the adjusted ellipticallens of the upward detection optics system and by adjusting apertureangles in two directions perpendicular to each other.

In order to obtain the abovementioned effects, the adjusted ellipticallens can be provided only in the upward detection optics system.

Effect 3

It is possible to achieve a detection optics system, which is assembledwith high density implementation by using a flat optical lens fordetection.

The adjusted elliptical lens with a small aperture angle in theelevation direction and a large aperture angle in the azimuth directioncan be installed in a small space in the elevation direction. As shownin FIG. 8, a plurality of the adjusted elliptical lenses 502 can beprovided with high density implementation in the elevation direction andwith a small gap between the adjusted elliptical lenses. The detectionoptics system can be arranged with high density implementation in theelevation direction and at an optimal elevation angle appropriate forcharacteristics of light scattered from the defect. The detection opticssystem is capable of detecting the defect with high efficiency. Inaddition, this arrangement makes it possible for the optics system todetect a small or minute defect with detection ability improved.Furthermore, the arrangement makes it possible to install a plurality ofthe detectors to categorize defects. The method for categorizing defectswill be described in Effect 4.

Effect 4

It is possible to discriminate scattering characteristics and categorizedefects by using the plurality of detectors.

The light scattered from the defect varies in elevation angle, at whichthe scattered light is reflected, depending on the type of the defect.The types of the defects include an attached foreign material, ascratch, a short circuit occurring in a circuit pattern, a disconnectionoccurring in a circuit pattern, and a pit. Although it is necessary todetect and categorize such defects, the directions of light scatteredfrom such defects may be different depending on the type of the defect.For example, as shown in FIGS. 10A to 10C, three or more of the adjustedelliptical lenses 502 are installed at positions defined by the sameazimuth directions and elevation directions different from each other,or at positions defined by the same elevation direction and azimuthdirections different from each other, or at positions defined by azimuthdirections different from each other and elevation directions differentfrom each other to achieve an oblique detection optics system 503 withhigh density implementation. The oblique detection optics system 503 isadapted to detect light scattered from a defect present on the sample atan acute angle with the surface of the sample. The plurality ofdetectors 501 are capable of detecting light scattered from the defect.This makes it possible to determine a direction of traveling of thelight scattered at a low elevation angle and at a high elevation angleand to categorize the defect based on the direction of the scatteredlight. In addition, the direction of the scattered light to be detectedvaries depending on the direction of the illumination light beam,resulting in the fact that information on the categories can beincreased.

FIGS. 11A to 11C are diagrams to compare a case example in which asample is detected by using light incident on the sample at a highelevation angle with respect to the surface of the sample, with a caseexample in which a sample is detected by using light incident on thesample at a low elevation angle with respect to the surface of thesample. As shown in FIGS. 11A to 11C, it is understood that the types ofthe defects can be discriminated based on the elevation angle of theillumination light beam with respect to the surface of the sample, anazimuth angle of the detected light with respect to a specifieddirection, and the elevation angle of the detected light with respect tothe surface of the sample. A polarization state of the light toilluminate the defect is selected from among S-polarized light,P-polarized light, circularly-polarized light, and non-polarized lightto ensure that a condition for spatial distribution of the scatteredlight is varied. By using the polarization condition, the ability toestimate the type of the detected defect can be improved. The pluralityof detectors provide a great effect to improve the ability to categorizethe defect.

Effect 5

An anisotropic aperture of the detection optics system is advantageousbased on conditions for illumination performed by the optics system forillumination to form a beam.

Here, a beam to be formed by the detection optics system is comparedwith the beam to be formed by the optics system for illumination. Asshown in FIG. 9, in the detection optics system, an elongated beam spotof the illumination light beam is formed without the illumination lightbeam being focused, the length of the illumination light beam beingperpendicular to the direction of scanning of the stage. Theillumination light beam is focused to concentrate on illumination powerin the direction (the elevation direction) perpendicular to thedirection of scanning of the stage. That is, the illumination light beamis incident on the surface of the wafer at an elevation angle withrespect to the surface of the wafer in order to inspect the wafer. Inthe case where the light is reflected on the wafer to be inspected, anaperture angle in the azimuth direction (horizontal direction isrequired to be large for the lens of the detection optics system as acondition necessary for detecting a defect (since the illumination lightis parallel light). However, it is not necessary that an aperture anglein the elevation direction be large for the lens of the detection opticssystem. In the case of using the adjusted elliptical lens, the conditionfor the aperture matches with the condition for the beam formationperformed by the optics system for illumination, and it is necessarythat the aperture of the detection optics system be based on thenumerical aperture (NA) of the optics system for beam formation, whichis provided in the optics system for illumination, resulting in the factthat the optics system can detect a defect with high efficiency.

It should be noted that use of some of the aperture angles of thedetection optics system makes it possible to efficiently detect adefect. The detection optics system is installed to obtain apertureangles in two directions perpendicular to each other and is capable ofdetecting a defect with high efficiency even if a part of the detectionoptics system having a circular lens with an isotropic aperture is usedto change the aperture angle. As shown in FIG. 12, when the scatteredlight is blocked by an upper half portion of an isotropic optical lens5020 for detection and a lower half portion of the isotropic opticallens 5020 is used as an aperture thereof, the aperture angle in the twodirections perpendicular to each other can be changed, resulting inimprovement of an effect to change an intensity ratio of a signal comingfrom a defect to a background signal. This can achieve an increase insensitivity for detection of the defect.

In addition, the upward detection optics system and the obliquedetection optics system can be installed at positions different fromeach other to achieve the best detection performance, respectively.

When the upward detection optics system and the oblique detection opticssystem are used to improve the sensitivity for detection of the defect,the two optics systems preferably measure the same locationsimultaneously to reduce a throughput time. In this case, the conditionsfor irradiation of the illumination light beam, such as an elevationangle, an azimuth angle, and polarization conditions, are limited to asingle type of the conditions. There are many cases where the optimalconditions for illumination vary depending on the defect to be detectedand on the combination of the upward detection optics system and theoblique detection optics system. It is necessary to change illuminationconditions for each of the two optics systems in order to detect adefect with high sensitivity under the optimal conditions forirradiation of the illumination light beam by using the upward detectionoptics system and the oblique detection optics system. As shown in FIG.13, each of the upward detection optics system and the oblique detectionoptics system simultaneously performs a single inspection under theillumination conditions for each of the upward detection optics systemand the oblique detection optics system, the illumination conditions forthe upward detection optics system being different from the illuminationconditions for the oblique detection optics system. The simultaneousinspections performed by the two detection optics systems make itpossible to detect a defect with high sensitivity. In this case, the twodetection optics systems are installed at positions different from eachother.

FIG. 14 is a diagram showing the configuration of the defect inspectionsystem applicable to the present invention. The defect inspection systemshown in FIG. 14 includes a stage section 300, an optics system 100 forillumination, an optics system (hereinafter referred to as a “upwarddetection optics system”) 200 for detection of light scattered upwardlywith respect to the surface of a sample, an optics system (hereinafterreferred to as a “oblique detection optics system”) 500 for detection oflight scattered obliquely with respect to the surface of the sample, anda control system 400. The stage section 300 is adapted to move a samplesuch as a wafer in an X-axis direction, Y-axis direction, and Z-axisdirection and to rotate around the Z-axis. The optics system 100 isadapted to irradiate illumination light beam on the sample for detectionof a defect. The upward detection optics system 200 is adapted to detectlight reflected from the sample. The oblique detection optics system 500is adapted to detect light reflected from the sample. The control system400 is adapted to execute arithmetic processing, signal processing, andthe like.

The stage section 300 has an X stage 301, a Y stage 302, a Z stage 303,a rotation stage 304, and a stage controller 305. The optics system 100for illumination has a laser source 101, a beam expander composed of aconcave lens 102 and a convex lens 103, a beam formation sectioncomposed of an optical filer group 104 and a mirror 105, and first,second and third beam spot imaging sections 110, 120 and 130. The firstbeam spot imaging section 110 includes an optical branching element (ora mirror) 106, an illumination lens 107 having a conic surface, andmirrors 108 and 109. The optical filter group 104 includes a neutraldensity (ND) filter and a wavelength plate.

As the laser source 101, a third-harmonic generation (THG) of a highpower YAG laser is preferably used. The THG has a wavelength of 355 nm.It is not necessary that the THG necessarily have the wavelength of 355nm. In addition, it is not necessary that the YAG laser and the THG arenecessarily used as the laser source 101. Specifically, as the lasersource 101, an Ar laser, a nitrogen laser, an He—Cd laser, an excimerlaser, or the like may be used.

The upward detection optics system 200 has a detection lens 201, a spacefilter 202, an imaging lens 203, a zoom lens group 204, aone-dimensional detector (image sensor) 205, a space filter controller207, and a zoom lens controller 208. The oblique detection optics system500 has a one-dimensional detector (image sensor) 501, an objective lens502, a space filter 503, and an imaging lens 504. The one-dimensionaldetector 205 may be a time delay integration (TDI) sensor. The controlsystem 400 has an arithmetic processor 401, a signal processor 402, anoutput section 403, and an input section 404. The arithmetic processor401 has a central processing unit (CPU) and the like and controls adriving system such as a motor, coordinates, and the sensors. The signalprocessor 402 has: an analog-digital converter, a data memory capable ofdelaying data, a differential processing circuit for calculating adifference between signals supplied from chips, a memory for temporarilystoring a signal indicative of the difference between the signalssupplied from the chips, a threshold calculator for setting a patternthreshold, comparator, and the like.

The output section 403 is adapted to store a result of detection of adefect such as a foreign material and to output or display the result ofdetection of the defect. The input section 404 is adapted to input acommand and data to the arithmetic processor 401 in accordance with anoperation performed by a user. A system of coordinates is shown at thelower left of FIG. 14. In FIG. 14, an X axis and a Y axis are plotted ina horizontal plane, and a Z axis is plotted in a vertical direction. Thehorizontal plane is parallel to the surface of the sample, and thevertical direction is perpendicular to the surface of the sample. Theupward detection optics system 200 has an optical axis parallel to the Zaxis, and the oblique detection optics system 500 has an optical axisparallel to the horizontal plane xz.

The three beam spot imaging sections 110, 120 and 130 of the opticssystem 100 for illumination will be described with reference to FIGS. 15and 16. FIG. 15 is a top view of a sample 1 which is a wafer. In FIG.15, an illumination light beam 11 is irradiated on the surface of thesample 1 from the X-axis direction through the first beam spot imagingsection 110. An illumination light beam 12 is irradiated on the surfaceof the sample 1 from a direction inclined at an angle of 45 degrees withrespect to the Y-axis direction in the horizontal plane through thesecond beam spot imaging section 120, and an illumination light beam 13is irradiated from a direction inclined at an angle of 45 degrees withrespect to the Y-axis direction and perpendicular to the direction oftraveling of the illumination light beam 12 in the horizontal planethrough the third beam spot imaging section 130. The oblique detectionoptics system 500 is installed at a position on the opposite side of thefirst beam spot imaging section 110 with respect to the sample 1.

The illumination light beams 11, 12 and 13 are irradiated on the surfaceof the sample 1 at a predetermined elevation angle α with respect to thesurface of the sample 1. In particular, the elevation angle α of theillumination light beams 12 and 13 can be reduced to decrease the amountof light to be detected scattered from the bottom surface of a thintransparent film. The illumination light beams 11, 12 and 13 form anelongated beam spot 3 on the sample 1. The length of the beam spot 3 isextended in the Y-axis direction, and is larger than a diameter of alight receiving area 4 of the one-dimensional detector 205 provided inthe upward detection optics system 200. A description will be made ofthe reason for installations of the three beam spot imaging sections110, 120 and 130 in the optics system 100 for illumination. When anangle formed between the direction of traveling of the illuminationlight beam 11 and the direction of traveling of the illumination lightbeam 12 in the horizontal plane is β1, and an angle formed between thedirection of traveling of the illumination light beam 13 and the X-axisdirection is β2, β1=β2=45 degrees in the embodiment of the presentinvention. This arrangement makes it possible to prevent lightdiffracted in zero order from a non-repetitive pattern on a substrate ofthe sample 1 from being incident on the objective lens 201 of the upwarddetection optics system 200.

The non-repetitive pattern on the substrate of the sample 1 is mainlycomposed of linear patterns each having lines, which are parallel orperpendicular to the lines of another one of the linear patterns. Thelines of each of the linear patterns are parallel to the X-axisdirection or the Y-axis direction. The pattern formed on the substrateof the sample 1 projects, and a recessed portion is formed between theadjacent linear patterns. The illumination light beams 12 and 13 emittedfrom directions inclined at an angle of 45 degrees with respect to the Xand Y axes are blocked by the circuit pattern which projects, and cannotbe irradiated on the recessed portion formed between the linearpatterns. The beam spot imaging section 110 is provided on the X axis toemit the illumination light beam 12 for detection of a defect. Thus, theillumination light beam 11 can be irradiated on the recessed portionbetween the adjacent linear patterns to detect a defect such as aforeign material present on the recessed portion. The sample may berotated by 90 degrees based on the direction of the lines of the linearpattern to ensure that the sample is inspected. Alternatively, theillumination light beam 11 may be irradiated on the sample from theY-axis direction to inspect the sample. When the illumination light beamis irradiated on the sample in the X-axis direction, i.e., on therecessed portion formed between the adjacent linear patterns as is theillumination light beam 11, it is necessary that the detector blockzero-order diffracted light to ensure not to detect the zero-orderdiffracted light. To block the zero-order diffracted light, the spacefilter 202 is provided.

Next, with reference to FIGS. 16A, 16B and 17, a method for forming anelongated beam spot 3 will be described. Each of FIGS. 16A and 16B showsthe laser source 101, the concave lens 102, the convex lens 103 and theillumination lens 104, which are provided in the optics system 100 forillumination. The other elements 105, 106, 107, 108, and 109 of theoptics system 100 are omitted in FIGS. 16A and 16B. The illuminationlens 104 is cylindrical, that is, has a conic shape. As shown in FIG.16A, the focal length of the illumination lens 104 is linearly varied ina longitudinal direction thereof. As shown in FIG. 16B, the illuminationlens 104 has a cross section of the shape of a flat convex lens.

As shown in FIG. 17, the illumination light beam is incident on thesample 1 at an elevation angle α1 with respect to the surface of thesample 1 with a reduction in the aperture of the illumination lens inthe Y-axis direction, the illumination light beam being collimated inthe X-axis direction. The illumination light beam forms an elongatedbeam spot 3 on the surface of the sample 1. In FIG. 17, an angle of theillumination light beam with respect to the surface of the sample 1 isα1 and an image of the illumination light beam irradiated on the sample1 is formed in a direction inclined at an angle of β1 with respect tothe X-axis direction. The use of the illumination lens 104 makes itpossible to collimate the illumination light beam in the X-axisdirection and to form the image of the illumination light beam in thedirection inclined at the angle of β1, which is approximately 45degrees, with respect to the X-axis direction.

Next, a description will be made of an example of the configuration ofthe three beam spot imaging sections 110, 120 and 130 in the opticssystem 100 for illumination with reference to FIG. 18. In FIG. 18, thelaser source 101 emits a laser beam, which is divided into two lightbeams by a first optical element 141 for branching of light such as halfmirror. One of the light beams is reflected by a mirror 142 and a mirror143 and incident on a concave lens 144 constituting the first beam spotimaging section 110. In this way, the illumination light beam 11 isgenerated by the first beam spot imaging section 110.

The other one of the light beams is divided into two light sub-beams bya second optical element 145 for branching of light such as a halfmirror, the light sub-beams directing to light paths different from eachother. One of the light sub-beams is reflected by a mirror 146 andincident on a concave lens 147 constituting the second beam spot imagingsection 120. In this way, illumination light beam 12 is generated by thesecond beam spot imaging section 120. The other one of the lightsub-beams is incident on a concave lens 148 constituting the third beamspot imaging section 130. In this way, illumination light beam 13 isgenerated by the third beam spot imaging section 130.

When the first optical element 141 is removed from the light path orreplaced with an optical element 141 a, which passes light withoutreflecting and branching the light, the illumination light beam 11 isnot generated by the first beam spot imaging section 110. That is, theillumination light beam 12 and the illumination light beam 13 are onlygenerated by the second beam spot imaging section 120 and the third beamspot imaging section 130, respectively. In addition, when the firstoptical element 141 is removed from the light path or replaced with theoptical element 141 a, and the second optical element 145 is replacedwith a mirror 145 a for reflecting light without passing and branchingthe light, the illumination light beam 13 is only generated by the thirdbeam spot imaging section 130.

When the first optical element 141 is removed from the light path orreplaced with the optical element 141 a, and the second optical element145 is removed from the light path or replaced with an optical element,which passes light without reflecting and branching the light, theillumination light beam 12 is only generated by the second beam spotimaging section 120. When the first optical element 141 is installed andthe second optical element 145 is replaced with the mirror 145 a, theillumination light beam 11 and the illumination light beam 13 are onlygenerated by the first beam spot imaging section 110 and the third beamspot imaging section 130, respectively.

When the first optical element 141 is installed, and the second opticalelement 145 is removed or replaced with the optical element, whichpasses light without branching and reflecting the light, theillumination light beam 11 and the illumination light beam 12 are onlygenerated by the first beam spot imaging section 110 and the second beamspot imaging section 120, respectively. As described above, theillumination light beams 11, 12 and 13 can be selectively generated bythe three beam spot imaging sections 110, 120 and 130.

Next, with reference to FIG. 19, a description will be made of theupward detection optics system 200. In FIG. 19, the illumination lightbeam is irradiated on the sample 1 to form an elongated beam spot 3, andreflected by and scattered from the sample 1. The light is output fromupper and bottom surfaces of the transparent thin film, a circuitpattern present on the substrate of the sample 1, and a defect such as aforeign material. The output light is received by the detector 205 viathe detection lens 201, the space filter 202 and the imaging lens 203included in the upward detection optics system 200, andphotoelectrically converted by the detector 205. Since the illuminationintensity (power) of flux of light emitted from the laser source 101 canbe controlled by the ND filter of the optical filter group 104 or bycontrolling laser power, a dynamic range of output of the detector 205can be controlled.

Next, the space filter 202 will be described. The illumination lightbeam is irradiated on the repetitive pattern present on the sample 1 toform an interference fringe of diffracted light. When the detector 205receives the interference fringe of diffracted light, an error signal isgenerated. In this case, the detector 205 cannot detect a defect such asa foreign material. The space filter 202 is arranged in a spatialfrequency domain of the objective lens 201, i.e., at a location(corresponding to an exit pupil) of a Fourier-transformed image in orderto block the Fourier-transformed image based on the light diffracted bythe repetitive pattern.

As described above with reference to FIGS. 5A and 5B, the chip formed onthe wafer includes a repetitive pattern, a non-repetitive pattern, and apart not having a pattern in general. The line width of the repetitivepattern is varied depending on the circuit pattern. It is general thatas the space filter 202, a light blocking pattern is set to block lightfrequently diffracted by the repetitive pattern. As the space filter202, the light blocking pattern may be changed. Alternatively, as thespace filter 202, a plurality of light blocking patterns different fromeach other may be provided. In any of the above cases, the lightblocking pattern may be changed or replaced based on the circuit patternto block the diffracted light.

As described above, when the illumination light beam 11 is irradiated onthe recessed portion between the linear patterns in the X-axisdirection, it is necessary that zero-order diffracted light be blockedby the space filter 202. It is preferable that the space filter 202 beinstalled to block not only the zero-order diffracted light but alsohigh-order diffracted light.

Next, a description will be made of a method for adjusting detectionsensitivity based on the size of a defect such as a foreign material,which is to be detected. When the size of each of pixels of theone-dimensional detector (image sensor) 205, such as the TDI sensor, isreduced, the detector 205 can detect a smaller defect such as a foreignmaterial although the throughput of the detector 205 is reduced, thesize of each of the pixels being measured based on an image formed onthe sample 1 by the pixels of the detector 205. In order to vary thesize of the image formed on the sample 1 by the pixels of theone-dimensional detector (image sensor) 205, three types of the upwarddetection optics systems 200 are prepared.

To detect a defect such as a foreign material, having a length or adiameter of 0.1 μm or less, the upward detection optics system 200having a small pixel size measured based on an image formed on thesample 1 by the pixels thereof is selected for use. Lenses of the zoomlens group 204 may be selected to ensure that the configuration of theupward detection optics system 200 having the small pixel size isachieved. For example, the configuration of the lenses of the zoom lensgroup 204 may be designed to ensure that the length of a light path fromthe sample 1 to the one-dimensional detector 205 such as the TDI sensoris not varied. If it is difficult to achieve the configuration of thezoom lens group 204, a mechanism for controlling the distance betweenthe sample 1 and the one-dimensional detector 205 (image sensor) may beused in addition to the selection of the lenses of the zoom lens group204. In addition, the one-dimensional detector 205 having a differentpixel size may be used.

Next, a description will be made of the oblique detection optics system500 with reference to FIG. 19. The optical axis of the oblique detectionoptics system 500 is inclined at a predetermined angle β with respect tothe surface of the sample 1. To reduce the amount of light which isscattered from the bottom surface of the transparent thin film anddetected, the optical axis of the oblique detection optics system 500needs to be set to ensure that light output at angles from 80 to 90degrees with respect to the surface of the sample 1 is detected. Theadjusted elliptical lens 502 according to the present invention can beused to ensure that the oblique detection optics system 500 is installedat a position corresponding to a low elevation angle with respect to thesurface of the sample 1. Light reflected from the elongated beam spotformed on the sample 1 is detected by the one-dimensional detector(image sensor) 501 via the objective lens 502, the space filter 503 andthe imaging lens 504.

In the example shown in FIG. 19, the one-dimensional detector (imagesensor) 501 is used to detect an image of the elongated beam spot. Thespace filter 503 is adapted to block an interference fringe of lightdiffracted from the repetitive pattern present on the sample in the samemanner as the space filter 202.

The outline of a method for detecting a defect such as a foreignmaterial will be described. In step S101 shown in FIG. 19, the controlsystem receives a signal from the one-dimensional detector (imagesensor) 205 of the upward detection optics system 200 to executehigh-speed parallel image processing on the received signal. In stepS103, the control system acquires an image to be inspected. In stepS104, the control system acquires an image adjacent to the image to beinspected after delay processing in step S102. Next, in step S105, thecontrol system executes image alignment processing to align the image tobe inspected and the adjacent image. Then, in step S106, the controlsystem compares the image to be inspected with the adjacent image.

In step S107, the control system determines a defect based on the resultof the comparison. In step S201, the control system receives a signalfrom the one-dimensional detector (image sensor) 501 of the obliquedetection optics system 500 to execute high-speed parallel imageprocessing on the received signal. Steps S202 to S207 are the same asstep S102 to S107. The control system combines information on the defectbased on the result of the determination in step S107 with informationon the defect based on the result of the determination in step S207 tomake a comprehensive determination. Lastly, in step S108, the controlsystem combines the defect detected by the upward detection opticssystem 200 with the defect detected by the oblique detection opticssystem 500 to generate a defect map.

In the example shown in FIG. 19, the defect inspection system performsthe defect determination in step S107 and the defect determination instep S207. The defect inspection system may perform both defectdeterminations in a single step to generate a defect map.

Specifically, as shown in FIG. 20, the control system may compare theresult of the comparison in step S106 with the result of the comparisonin step S206 to perform the comprehensive determination in step S107,and then generate a defect map in step S108.

Next, a description will be made of the case where the defect inspectionsystem according to the present invention inspects a defect under aplurality of conditions. The inspection is performed for the purpose ofincreasing the dynamic range, for example. Three conditions are setbased on power (high power, medium power, and low power) of theillumination light. The three conditions correspond to a priority on anarea, a standard, and a priority on sensitivity.

Under the three conditions, the defect inspection system inspects thesurface of the wafer, which is the sample, and combines results of theinspections to generate an inspection result map (which is a drawing inwhich a mark indicative of a defect such as a foreign material detectedfrom the sample 1 is plotted on position coordinates). The inspectionresult map may be replaced with a coordinates list of defects, or a listor map expressing levels of detection signals obtained from defects. Thedefect inspection system performs the inspection for the purpose ofdetecting a more microscopic scratch or defect such as a foreignmaterial, in addition to the purpose of increasing the dynamic range. Inthis case, conditions for the inspection includes scanning time of eachof the stages 301 and 302, angles α1, β1 (including a value of zero) andβ2 (including a value of zero) of the illumination light beam generatedby the optics system 100, and the presence of the wavelength plate 104,and the like.

Next, a description will be made of a production line and a productionmethod for manufacturing a semiconductor and the like by using thedefect inspection system according to the present invention. Thesemiconductor production line using the defect inspection systemaccording to the present invention includes a manufacturing process, aprobe inspection process, an inspection system and a data analysissystem. The manufacturing process, especially, a process affecting theyield is always monitored by the inspection system including the defectinspection system according to the present invention. When anyabnormality in the processes is detected by the monitoring performed bythe inspection system, the process or the system, which causes theabnormality, is identified by the inspection system.

In order to inspect a foreign material or a defect such as a foreignmaterial attached to a top surface of the sample in a desired processwith high accuracy of identification, it is preferable that the defectinspection system according to the present invention perform theinspection of a defect such as a foreign material before and after thedesired process to calculate a logical difference between a result ofthe defect inspection after the desired process and a result of thedefect inspection before the desired process.

It is not always that only a defect such as a foreign material occurringin the desired process can be detected based on the logical difference.The reason is described as follows. For example, a film is formed on thesurface of the defect such as a foreign material in a film formationprocess or the like, resulting in an increase in the size of the defect.This improves inspection sensitivity. As a result, a defect presentbefore the film formation process is inspected after the film formationprocess. More specifically, the defect present before the film formationprocess is not inspected before the film formation process and isinspected after the film formation process, resulting in the fact thatit is mistakenly determined that the defect occurs in the film formationprocess.

In the defect inspection system according to the present invention,however, the oblique detection optics system can be installed at aposition corresponding to a low elevation angle and is capable ofdetecting only a defect present on the surface of the sample with areduction in the amount of light scattered from a background defect.This makes it possible to eliminate an incorrect determination.

As described above, the defect inspection system according to thepresent invention is capable of improving the efficiency ofillumination. Also, the defect inspection system is capable ofdetecting, with high sensitivity, a foreign material present on thesurface such as a LSI pattern by using the space filter and optimizingthe angle of the traveling direction of the illumination light withrespect to the surface of the sample. In addition, the defect inspectionsystem is capable of reducing light diffracted from a pattern present onthe substrate. Furthermore, the defect inspection system is capable ofsetting a low detection threshold for separating background light fromlight which is reflected on a foreign material present on the surface ofthe sample and is detected, in order to avoid an effect of an increaseand reduction in the amount of light due to thin film interference ofdiffracted light caused by a variation in the thickness of thetransparent thin film.

Thus, the defect inspection system is capable of detecting a microscopicforeign material present on the surface of the sample having a length ordiameter of about 0.1 μm with high sensitivity and preventing incorrectdetection.

In the defect inspection system according to the present invention,light scattered from a foreign material present on the surface of thesubstrate and light scattered from an internal pattern can be separatedfrom each other. The defect inspection system performs the inspectionfor each process for producing a wafer to determine a process causing aforeign material, making it possible to quickly identify a source of thedefect.

In addition, the defect inspection system according to the presentinvention is capable of simultaneously obtaining outputs from thedetector of the upward detection optics system and from the detector ofthe oblique detection optics system in a single inspection to obtain thedouble of the amount of information compared with conventionaltechniques. This makes it possible to reduce the throughput time byhalf.

Furthermore, the defect inspection system according to the presentinvention has a plurality of the detectors capable of detecting lightscattered from a foreign material in a direction different from that oflight to be detected by the conventional techniques. Since the defectinspection system can obtain the double of the amount of information andthe double of the value of the information, the defect inspection systemcan determine the size and the shape of the foreign material moreaccurately than the conventional techniques.

It should be noted that, as shown in FIG. 7B, a plurality of theadjusted elliptical lenses 10B can be installed in the same optical axisthereof to correct aberration. In this case, when the elevation angle is12 degrees, seven to fifteen of the adjusted elliptical lenses can beinstalled.

1. A defect inspection system comprising: light irradiation unit forirradiating an illumination light beam on the surface of a sample to beinspected from a direction inclined with respect to a normal to thesurface of the sample; detection unit for detecting light scattered fromthe surface of the sample irradiated by the illumination light beam; anoptical lens arranged between the sample and the detection unit andfocusing the scattered light on the detection unit, the optical lenshaving a length in an elevation direction parallel to a normal to adirection of traveling of the light scattered from the surface of thesample, and a length in an azimuth direction parallel to the surface ofthe sample, the length in the azimuth direction being larger than thelength in the elevation direction; and defect determination unit fordetermining a defect present on the surface of the sample based on thescattered light detected by the detection unit.
 2. The defect inspectionsystem according to claim 1, wherein the optical lens is an adjustedelliptical lens which has a shape obtained by cutting a circular lensalong two cutting lines parallel to each other to form two straightsides parallel to each other and has two elliptical arcs locatedsymmetrically to a central axis thereof, which is perpendicular to thetwo straight sides separated a distance smaller than the maximum lengthof an imaginary line extending between the two elliptical arcs, theimaginary line being parallel to the two straight sides.
 3. The defectinspection system according to claim 1, wherein a plurality of theoptical lenses are provided; and a plurality of detectors are provided,each of which detects scattered light passing through each respectiveoptical lens paired with the detector.
 4. The defect inspection systemaccording to claim 3, wherein the plurality of optical lenses arearranged in the elevation direction.
 5. The defect inspection systemaccording to claim 3, wherein the plurality of optical lenses arearranged in the azimuth direction.
 6. The defect inspection systemaccording to claim 3, wherein the plurality of optical lenses arearranged in the elevation direction and the azimuth direction.
 7. Thedefect inspection system according to claim 3, wherein the lightirradiation unit irradiates the illumination light beam on the surfaceof the sample in a plurality of azimuth directions.
 8. The defectinspection system according to claim 1, wherein a plurality of theoptical lenses are arranged in the same optical axis thereof to correctaberration.
 9. A defect-inspection system comprising: light irradiationunit for irradiating an illumination light beam on the surface of asample to be inspected from a direction inclined with respect to anormal to the surface of the sample; first detection unit for detectinglight scattered from the surface of the sample irradiated by theillumination light beam; a first optical lens arranged between thesample and the first detection unit in a direction inclined with respectto a normal to the surface of the sample and focusing the scatteredlight on the first detection unit, the first optical lens having alength in an elevation direction parallel to a normal to a direction oftraveling of the light scattered from the surface of the sample, and alength in an azimuth direction parallel to the surface of the sample,the length in the azimuth direction being larger than the length in theelevation direction; second detection unit for detecting light scatteredfrom the surface of the sample irradiated by the illumination lightbeam; a second optical lens arranged between the sample and the seconddetection unit in a direction of the normal to the surface of the sampleand focusing the scattered light on the second detection unit; anddefect determination unit for determining a defect present on thesurface of the sample based on the scattered light detected by the firstand second detection unit.
 10. The defect inspection system according toclaim 9, wherein the second optical lens is arranged in a directioninclined with respect to a normal to the surface of the sample and has alength in the elevation direction and a length in the azimuth direction,the length in the azimuth direction being larger than the length in theelevation direction.
 11. The defect inspection system according to claim1, comprising a space filter arranged between the optical lens and thedetection unit and blocking light diffracted by a repetitive patternformed in a circuit pattern present on the sample to be inspected. 12.The defect inspection system according to claim 1, comprising aplurality of the optical lenses, each of which has a magnification, themagnifications of each of the optical lenses being different from eachother, wherein each of the magnifications is selected based on a defectto be detected.
 13. The defect inspection system according to claim 1,wherein the detection unit is a linear image sensor.
 14. The defectinspection system according to claim 10, wherein the second detectionunit is a linear image sensor.